This invention relates to an improvement in combustion control apparatus, and particularly to apparatus for preventing smoke due to malfunction of an exhaust gas analysis device or slow response of the normal control apparatus to unfavorable combustion conditions indicated by the device.
In combustion processes in which the BTU content of the fuel supplied is likely to vary, it is known to adjust the ratio of fuel and air based on a measure of the combustion conditions from analysis of the oxygen content of the stack gas. This is particularly necessary where a boiler may be fed with oil or natural gas or blast furnace gas or combinations of them which can vary greatly in relative proportions. Even with such controls smoking often occurs.
U.S. Pat. No. 3,503,553 Schomaker shows apparatus for providing a minimum supply of air to the process and metering of the remaining air supply based on an oxygen controller in order to prevent dangerous conditions such as an excessive amount of fuel available upon startup of a boiler which can be dangerous. U.S. Pat. No. 2,562,507 shows apparatus for increasing the supply of air for combustion in response to an optical device which indicates smoke has formed in the stack. Neither reference is effective for preventing formation of smoke.
It is therefore a primary object of this invention to prevent formation of smoke in combustion processes utilizing stack gas analyses for metering control.